JP2016183273A - Porous polyimide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous polyimide film that suppresses development of cracks and is suitable for a cell electrode material such as a cell separator, a separation membrane, a low dielectric constant material, or the like.SOLUTION: The porous polyimide film is obtained through steps of: forming a coating film that contains a polyimide precursor solution prepared by dissolving a polyimide precursor in a water-soluble solvent and contains 0.1 to 5 mass% of non-crosslinking resin particles incapable of dissolving in the solution, and then drying and heating the coating film to imidize to form a polyimide film; and removing the non-crosslinking resin particles by dissolving the particles in an organic solvent to produce pores.SELECTED DRAWING: None

Description

  The present invention relates to a porous polyimide film.

  Polyimide resin is a material having excellent properties such as mechanical strength, chemical stability, and heat resistance, and a porous polyimide film having these properties has attracted attention.

For example, Patent Document 1 discloses a lithium secondary battery comprising a porous polyimide resin film having a porosity of 60% or more, a pore having a three-dimensional regular array structure, and pores connected to each other. A separator is described.
Patent Document 2 describes an organic porous body having pores made of polyimide and an ionic conductor holding an electrolyte material containing a cation component and an anion component in the pores.
In Patent Document 3, a varnish is produced by mixing polyamic acid or polyimide, silica particles and a solvent to produce a varnish, or polymerizing polyamic acid or polyimide in a solvent in which silica particles are dispersed to produce a varnish. After the varnish produced in the production process is formed on the substrate, the imidization is completed to produce a polyimide-silica composite film, and the polyimide-silica composite film produced in the composite film production process A method for producing a porous polyimide film having a silica removing step for removing silica is described.
Patent Document 4 discloses a porous silica mold produced by a porous silica mold production process for obtaining a porous silica mold after filling with silica particles and sintering, and a porous silica mold produced by the porous silica mold production process. A process for producing a porous polyimide having a polyimide filling step of filling the voids with polyimide and a silica removal step of removing the silica from a porous silica mold filled with the polyimide to obtain a porous polyimide is described.

Patent Document 5 discloses a positive electrode, a negative electrode, and a separator layer including a porous polyimide film having an average pore diameter of 5 μm or less, which is formed into a porous film by phase separation after solution application of polyimide or a polyimide precursor. , Non-aqueous electrolyte secondary batteries are described.
Patent Document 6 includes a step of preparing a resin composition for a film by mixing a heat-resistant resin such as polyimide, a heat extinguishing resin particle containing a polyoxyalkylene resin, and a solvent, and a resin composition for a film. The porous polyimide film obtained by the manufacturing method of the porous resin which has the process to form and the process to heat the formed resin composition for films is described.
In Patent Document 7, a polyimide precursor solution is made into a film using a solution in which a resin such as water-soluble polyethylene glycol is dissolved, and then contacted with a poor solvent such as water to precipitate polyamic acid and make it porous. Methods for promoting and imidizing are also described.

Japanese Patent No. 5331627 JP 2008-034212 A JP 2012-107144 A JP 2011-111470 A JP 10-302749 A JP 2010-024385 A JP 2014-240189 A

  The subject of this invention is providing the porous polyimide film by which generation | occurrence | production of the crack was suppressed compared with the porous polyimide film which contains only a polyimide resin as resin.

  In order to achieve the above object, the following invention is provided.

The invention according to claim 1
It is a porous polyimide film containing a polyimide resin and a non-crosslinked resin other than polyimide resin and having a spherical pore.

The invention according to claim 2
2. The porous polyimide film according to claim 1, wherein the content of the non-crosslinked resin other than the polyimide resin is 0.1% by mass or more and 5% by mass or less based on the entire porous polyimide film.

The invention according to claim 3
The porous polyimide film according to claim 1 or 2, wherein the non-crosslinked resin other than the polyimide resin is a non-crosslinked resin soluble in a solvent that does not dissolve the polyimide resin.

The invention according to claim 4
After forming a coating film containing a polyimide precursor solution in which a polyimide precursor is dissolved in an aqueous solvent and non-crosslinked resin particles not dissolved in the polyimide precursor solution, the coating film is dried, and the polyimide A first step of forming a coating comprising a precursor and the non-crosslinked resin particles;
The second step of heating the coating to imidize the polyimide precursor to form a polyimide film, and removing the non-crosslinked resin particles with an organic solvent that dissolves the non-crosslinked resin particles. A second step including:
It is a porous polyimide film as described in any one of Claims 1-3 obtained by the manufacturing method of the porous polyimide film which has this.

According to the invention which concerns on Claim 1, compared with the porous polyimide film which contains only a polyimide resin as resin, the porous polyimide film by which generation | occurrence | production of a crack is suppressed is provided.
According to the invention which concerns on Claim 2, generation | occurrence | production of a crack is suppressed compared with the case where content of non-crosslinked resin other than a polyimide resin is less than 0.1 mass% with respect to the whole porous polyimide film. A porous polyimide film is provided.
According to the invention of claim 3, the resin includes a non-crosslinked resin that dissolves in a solvent that does not dissolve the polyimide resin as a non-crosslinked resin other than the polyimide resin, as compared with a porous polyimide film that contains only a polyimide resin, and cracks. There is provided a porous polyimide film in which the generation of is suppressed.

  According to the invention which concerns on Claim 4, after forming the coating film containing a polyimide precursor solution and the non-crosslinked resin particle which is not melt | dissolved in a polyimide precursor solution, a coating film is dried and a polyimide precursor and non-crosslinking A first step of forming a coating containing resin particles, and a second step of heating the coating to imidize the polyimide precursor to form a polyimide film, including a process of removing non-crosslinked resin particles In the porous polyimide film obtained by the method for producing a porous polyimide film having the second step, as compared with the case where the solvent for dissolving the polyimide precursor solution in the polyimide precursor solution is only an organic solvent, A porous polyimide film in which generation of cracks is suppressed is provided.

It is process drawing which shows an example of the manufacturing method of the porous polyimide film of this embodiment. It is process drawing which shows another example of the manufacturing method of the porous polyimide film of this embodiment. It is process drawing which shows another example of the manufacturing method of the porous polyimide film of this embodiment.

  Embodiments that are examples of the present invention will be described below.

<Porous polyimide film>
The porous polyimide film according to the present embodiment contains a polyimide resin and a non-crosslinked resin other than the polyimide resin. The shape of the holes is spherical.
The porous polyimide film which concerns on this embodiment suppresses the crack of a porous polyimide film by the said structure. The reason is not clear, but is presumed as follows.

  The porous polyimide film may easily undergo volumetric shrinkage due to heat. Since a polyimide film is a rigid resin, residual stress due to volume shrinkage is likely to occur when pores are formed using a porous polyimide film made of only a polyimide resin, inorganic particles, or non-crosslinked resin particles, for example, as a template. In some cases, cracks may occur due to this.

  On the other hand, the porous polyimide film of the present embodiment includes a polyimide resin and a non-crosslinked resin other than the polyimide resin. And in addition to polyimide resin, when non-crosslinked resin other than polyimide resin is contained, non-crosslinked resin other than polyimide resin can easily relieve residual stress due to volume shrinkage, and the occurrence of cracks is suppressed. Conceivable. Furthermore, it is considered that the residual holes due to volume shrinkage can be more easily relaxed and the generation of cracks can be further suppressed due to the spherical pores.

  From the above, the porous polyimide film according to this embodiment is considered to suppress the occurrence of cracks in the porous polyimide film.

  The porous polyimide film having the above structure is formed in a water-based solvent after forming a coating film containing a polyimide precursor solution in which a polyimide precursor is dissolved and non-crosslinked resin particles not dissolved in the polyimide precursor solution. A first step of drying the coating film to form a coating film containing the polyimide precursor and the non-crosslinked resin particles; and heating the coating film to imidize the polyimide precursor to form a polyimide film. And a second step including a process of removing the non-crosslinked resin particles with an organic solvent that dissolves the non-crosslinked resin particles. It is preferable that it is a quality polyimide film.

  By this production method, the porous polyimide film can contain a non-crosslinked resin other than the polyimide resin, and it is presumed that generation of cracks is suppressed. The reason is not clear, but is presumed as follows.

  The polyimide film is, for example, a polyimide precursor solution (for example, N-methylpyrrolidone (hereinafter sometimes referred to as “NMP”) or N, N-dimethylacetamide (hereinafter referred to as “DMAc”) dissolved in an organic solvent. It may be obtained by applying a polyimide precursor solution in a state dissolved in a highly polar solvent, followed by thermoforming.

Conventionally, a porous polyimide film has been obtained using a polyimide precursor solution dissolved in an organic solvent. As a method for obtaining a porous polyimide film, for example, a method for obtaining a porous polyimide film having pores of a three-dimensional ordered array structure (3DOM structure) using a silica particle layer as a template, and silica particles in a polyimide precursor solution Examples include a method in which a coating is prepared using varnish in which is dispersed, and after the coating is fired, silica particles are removed to obtain a porous polyimide film. The porous polyimide film obtained by these methods is likely to crack. This is presumably because, in the imidization process, silica particles are difficult to absorb volume shrinkage, and thus distortion (residual stress) tends to occur in the film.
Furthermore, after forming into a film using a solution in which a resin such as water-soluble polyethylene glycol is dissolved in a polyimide precursor solution, it is brought into contact with a poor solvent such as water to precipitate polyamic acid and promote porosity, These methods are also known, but these methods utilize the fact that polyamic acid precipitates in a porous form by replacing a solvent such as NMP that dissolves polyamic acid with a poor solvent such as water. It is difficult to control the shape and size of the hole diameter.

  On the other hand, the porous polyimide film of this embodiment contains non-crosslinked resin other than polyimide resin. In the process of producing a porous polyimide film, in the imidization process of the polyimide precursor, the shape and size of the pore diameter can be easily controlled by removing the non-crosslinked resin particles with an organic solvent, and dissolved in the organic solvent. It is considered that the non-crosslinked resin component thus easily migrates into the polyimide resin. Thus, it is presumed that residual stress can be more easily relaxed by obtaining a porous polyimide film that has been imidized so as to contain a non-crosslinked resin other than a polyimide resin.

Moreover, the porous polyimide film obtained by the above production method of the present embodiment is likely to suppress variations in pore shape, pore diameter, and the like. The reason for this is presumed that the use of non-crosslinked resin particles in the production process effectively contributes to the relaxation of residual stress in the imidization process of the polyimide precursor.
Moreover, since the porous polyimide film obtained by the said manufacturing method of this embodiment has dissolved the polyimide precursor in the aqueous solvent, the boiling point of a polyimide precursor solution will be about 100 degreeC. As the coating containing the polyimide precursor and the non-crosslinked resin particles is heated, the imidization reaction proceeds after the solvent has been volatilized quickly. And before the deformation | transformation by a heat | fever arises, the non-crosslinked resin particle in a film loses fluidity and becomes insoluble in an organic solvent or water. Therefore, it is considered that the shape of the holes is easily maintained, and variations in the shape of the holes, the hole diameter, and the like are easily suppressed.

  When silica particles are used, it is necessary to use a chemical such as hydrofluoric acid in the treatment for removing the silica particles. Further, when a silica particle layer template is produced, the productivity is low and the cost is high because the silica particle layer is formed. In addition, when silica particles are used, it is considered that ions are likely to remain as impurities because chemicals such as hydrofluoric acid are used.

  On the other hand, since the porous polyimide film obtained by the manufacturing method of the present embodiment does not use silica particles, the process of obtaining the porous polyimide film is simplified. Moreover, since hydrofluoric acid is not used for the removal of non-crosslinked resin particles, it is suppressed that ions remain as impurities.

  Hereinafter, the porous polyimide film according to the present embodiment will be described together with the manufacturing method thereof.

  Specifically, the polyimide resin contained in the porous polyimide film according to the present embodiment is obtained by polymerizing tetracarboxylic dianhydride and a diamine compound to generate a polyimide precursor, and obtaining a solution of the polyimide precursor. , Obtained by imidization reaction. More specifically, it is obtained by imidization reaction using a polyimide precursor solution in which a polyimide precursor is dissolved in an aqueous solvent. For example, in an aqueous solvent, in the presence of an organic amine compound, tetracarboxylic dianhydride and a diamine compound are polymerized to form a resin (polyimide precursor) to obtain a polyimide precursor solution. It is not limited to this example. The polyimide precursor solution will be described later.

  Further, when the non-crosslinked resin other than the polyimide resin contained in the porous polyimide film according to the present embodiment is a porous polyimide film obtained in the above production method, the resin component of the non-crosslinked resin is left. is there. The non-crosslinked resin other than the polyimide resin may be contained in a state where the shape of the non-crosslinked resin particles is maintained, or may not have the shape of the non-crosslinked resin particles. That is, the porous polyimide film obtained by the manufacturing method according to the present embodiment only needs to contain a non-crosslinked resin component other than the polyimide resin. And the shape of the void | hole of the porous polyimide film obtained in the said manufacturing method has comprised the spherical form. The non-crosslinked resin particles will be described later.

  In the present embodiment, “does not dissolve” means that at 25 ° C., the target substance is substantially in the form of non-crosslinked resin particles with respect to the target liquid, and is 3% by mass or less. Including dissolution within the range.

(Method for producing porous polyimide film)
First, the manufacturing method of the porous polyimide film of this embodiment is demonstrated.
In the description of the manufacturing method, the same reference numerals are given to the same components in the drawings to be referred to. In the reference numerals of the drawings, 1 is a non-crosslinked resin particle, 2 is a binder resin, 3 is a substrate, 4 is a release layer, 5 is a polyimide precursor solution, 7 is a void, and 61 is an imidization of the polyimide precursor. Process coating (polyimide film) and 62 represent a porous polyimide film.

Although the manufacturing method of the porous polyimide film which concerns on this embodiment is not specifically limited, For example, the manufacturing method which has the 1st process and the 2nd process which are mentioned below is mentioned.
In the first step, after forming a coating film containing a polyimide precursor solution in which a polyimide precursor is dissolved and non-crosslinked resin particles not dissolved in the polyimide precursor solution in an aqueous solvent, It is a step of drying to form a film containing the polyimide precursor and the non-crosslinked resin.
The second step is a second step in which the film is heated to imidize the polyimide precursor to form a polyimide film, and the non-crosslinked resin is formed by an organic solvent that dissolves the non-crosslinked resin particles. It is a process including a process of removing particles.

  Hereinafter, although the manufacturing method shown in FIG. 1 (an example of the manufacturing method according to the present embodiment) will be described, the present invention is not limited to this.

(First step)
In the first step, first, a polyimide precursor solution in which a polyimide precursor is dissolved in an aqueous solvent is prepared. As the polyimide precursor solution in which the polyimide precursor is dissolved, for example, a polyimide precursor solution in which the polyimide precursor and the organic amine compound are dissolved is preferable. Hereinafter, as an example, an example using a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved will be described. Next, a coating film including a polyimide precursor solution and non-crosslinked resin particles that are not dissolved in the polyimide precursor solution is formed on the substrate. And the coating film formed on the board | substrate is dried, and the coating film containing a polyimide precursor and the said non-crosslinked resin particle is formed. In the following description, the non-crosslinked resin particles are non-crosslinked resin particles made of a non-crosslinked resin other than the polyimide resin.

  In the first step, as a method for forming a coating film containing a polyimide precursor solution and non-crosslinked resin particles not dissolved in the polyimide precursor solution on a substrate, specifically, the following method is used. Is mentioned.

  First, a non-crosslinked resin particle dispersion containing non-crosslinked resin particles that do not dissolve in the polyimide precursor solution, an organic solvent that does not dissolve the non-crosslinked resin particles, and a binder resin that dissolves in the organic solvent is prepared. Next, this non-crosslinked resin particle dispersion is applied onto a substrate and dried to form a non-crosslinked resin particle layer. The non-crosslinked resin particle layer formed on the substrate exists, for example, without the adjacent non-crosslinked resin particles being dissolved, and the adjacent non-crosslinked resin particles are bound by the binder resin. Yes. And the space | gap is formed between the non-crosslinked resin particles of a non-crosslinked resin particle layer (refer FIG. 1 (A)).

On the other hand, a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved in an aqueous solvent is prepared in advance.
Then, a previously prepared polyimide precursor solution is impregnated between the non-crosslinked resin particles of the non-crosslinked resin particle layer formed on the substrate. By impregnating the polyimide precursor solution between the non-crosslinked resin particles of the non-crosslinked resin particle layer, voids formed between the non-crosslinked resin particles of the non-crosslinked resin particle layer are filled with the polyimide precursor solution. In order to accelerate filling, it is also preferable to reduce the pressure in a state where the polyimide precursor solution and the non-crosslinked resin particles are in contact with each other to remove gas components between the voids. Then, this coating film is dried, and the coating film containing the polyimide precursor and the non-crosslinked resin particles is formed on the substrate (see FIG. 1B).

  The substrate on which the coating containing the polyimide precursor and non-crosslinked resin particles is formed is not particularly limited. Examples thereof include resin substrates such as polystyrene and polyethylene terephthalate; glass substrates; ceramic substrates; metal substrates such as iron and stainless steel (SUS); and composite material substrates in which these materials are combined. The substrate may be provided with a release layer by performing a release treatment with a silicone-based or fluorine-based release agent or the like, if necessary.

A method for producing the non-crosslinked resin particle dispersion is not particularly limited. For example, non-crosslinked resin particles that do not dissolve in the polyimide precursor solution, organic solvents that do not dissolve the non-crosslinked resin particles, and binder resins that dissolve in the organic solvent are weighed, mixed, and stirred. It is done. As the non-crosslinked resin particles, a dispersion of non-crosslinked resin particles dispersed in advance may be prepared, or a commercially available product that has been dispersed in advance may be prepared. When preparing a dispersion of non-crosslinked resin particles dispersed in advance, for example, the dispersibility of the non-crosslinked resin particles may be enhanced by at least one of an ionic surfactant and a nonionic surfactant.
The binder resin may be dissolved in advance in the above organic solvent, or may be dissolved by mixing non-crosslinked resin particles and an organic solvent.

  The ratio (mass ratio) between the non-crosslinked resin particles and the binder resin in the non-crosslinked resin particle dispersion is in the range of non-crosslinked resin particles: binder resin = 100: 0.5 to 100: 50. Is good. The range is preferably from 100: 1 to 100: 30, and more preferably from 100: 2 to 100: 20. Within this range, in the non-crosslinked resin particle layer formed by the non-crosslinked resin particle dispersion, the binder resin covers part or all of the surface of each non-crosslinked resin particle, and the adjacent non-crosslinked resin particles are adjacent to each other. Are bonded (primarily bonded state: including a so-called pseudo-bonded state). And it becomes easy to form the space | gap used as the state of an air layer between the non-crosslinked resin particles of a non-crosslinked resin particle layer.

The non-crosslinked resin particles are not particularly limited as long as they do not dissolve in the polyimide precursor solution. For example, non-crosslinked resin particles obtained by polycondensation of polymerizable monomers such as polyester resins and urethane resins, non-crosslinked resins obtained by radical polymerization of polymerizable monomers such as vinyl resins and olefin resins Particles. Non-crosslinked resin particles obtained by radical polymerization include (meth) acrylic resin, (meth) acrylic ester resin, styrene / (meth) acrylic resin, polystyrene resin, polyethylene resin non-crosslinked resin particles, and the like. .
The non-crosslinked resin particles are preferably non-crosslinked resin particles soluble in an organic solvent from the viewpoint of removal of non-crosslinked resin particles performed in the second step described later, and are soluble in a solvent in which the polyimide resin does not dissolve. Non-crosslinked resin particles are preferred. That is, the non-crosslinked resin other than polyimide contained in the porous polyimide film is preferably a non-crosslinked resin that is soluble in tetrahydrofuran, toluene, ethyl acetate, acetone, or the like.
Among these, the non-crosslinked resin particles are at least one selected from the group consisting of (meth) acrylic resin, (meth) acrylic ester resin, styrene / (meth) acrylic resin, and polystyrene resin. It is preferable.

  In the present embodiment, “(meth) acryl” means that both “acryl” and “methacryl” are included.

  In addition, when the non-crosslinked resin particles are, for example, vinyl resin particles, the synthesis method is not particularly limited, and known polymerization methods (emulsion polymerization, soap-free emulsion polymerization, suspension polymerization, miniemulsion polymerization, Radical polymerization methods such as microemulsion polymerization) can be applied.

  For example, when an emulsion polymerization method is applied to the production of vinyl resin particles, monomers such as styrenes and (meth) acrylic acids are added to water in which a water-soluble polymerization initiator such as potassium persulfate and ammonium persulfate is dissolved. In addition, if necessary, a surfactant such as sodium dodecyl sulfate, diphenyl oxide disulfonates and the like is added, and polymerization is carried out by heating while stirring to obtain vinyl resin particles.

Examples of the vinyl resin monomer include styrene and alkyl-substituted styrene (for example, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4 -Ethylstyrene, etc.), halogen-substituted styrene (for example, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), styrenes having a styrene skeleton such as vinylnaphthalene; methyl (meth) acrylate, (meth) acrylic Esters having vinyl groups such as ethyl acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, lauryl (meth) acrylate, 2-ethylhexyl (meth) acrylate; acrylonitrile, methacrylonitrile Vinyl nitriles such as vinyl methyl ether, vinyl isobut Vinyl ethers such as ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and vinyl isopropenyl ketone; acids such as (meth) acrylic acid, maleic acid, cinnamic acid, fumaric acid and vinyl sulfonic acid; ethyleneimine, vinyl Examples thereof include vinyl resin units obtained by polymerizing monomers such as bases such as pyridine and vinylamine.
Other monomers include monofunctional monomers such as vinyl acetate, bifunctional monomers such as ethylene glycol dimethacrylate, nonane diacrylate, decanediol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, etc. These polyfunctional monomers may be used in combination.
The vinyl resin may be a non-crosslinked resin using these monomers alone or a non-crosslinked resin which is a copolymer using two or more monomers.

  When the monomer used for the non-crosslinked resin constituting the vinyl resin particles contains styrene, the proportion of styrene in the total monomer component is preferably 20% by mass or more and 100% by mass or less, and 40% by mass or more and 100% by mass. A mass% or less is more preferable.

The average particle size of the non-crosslinked resin particles is not particularly limited. For example, the thickness is preferably 2.5 μm or less, desirably 2.0 μm or less, and more desirably 1.0 μm or less. Although it does not specifically limit as a minimum, It is good that it is 0.001 micrometer or more, Desirably 0.005 micrometer or more, More desirably, it is 0.01 micrometer or more.
In addition, the average particle diameter of the resin particles is a particle size range (channel) divided by using a particle size distribution obtained by measurement with a laser diffraction particle size distribution measuring apparatus (for example, LA-700 manufactured by HORIBA, Ltd.) The cumulative distribution is drawn from the small particle diameter side with respect to the volume, and the particle diameter that becomes 50% cumulative with respect to all particles is measured as the volume average particle diameter D50v.

  Examples of non-crosslinked resin particles include polymethyl methacrylate (MB-series, manufactured by Sekisui Plastics Co., Ltd.), (meth) acrylic acid ester / styrene copolymers (FS-series: manufactured by Nippon Paint Co., Ltd.), and the like. It is done.

  The binder resin is not particularly limited as long as it is soluble in an organic solvent and not soluble in a polyimide precursor solution. For example, acetal resin such as polyvinyl butyral resin; polyamide resin such as nylon; polyester resin such as polyethylene terephthalate and polyethylene naphthalate; polyolefin resin such as polyethylene and polypropylene; vinyl such as acrylic resin, polyvinyl chloride resin and polyvinylidene chloride resin Resin; polyurethane resin; polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, and the like. Polyvinyl acetal resin and aliphatic polyamide resin are preferred.

  Examples of organic solvents in which the non-crosslinked resin particles do not dissolve include alcohols such as methanol, ethanol, and ethylene glycol; cellosolves such as ethylene glycol monomethyl ether; hydrocarbons such as hexane; ketones such as acetone; aromatics such as toluene And the like; esters such as ethyl acetate; and nitriles such as acetonitrile.

  Among these, alcohols and cellosolves are preferable from the viewpoint of maintaining the shape of the non-crosslinked resin particles, and as the binder resin, resins soluble in alcohols and cellosolves (for example, acetal resins and polyamide resins) are used. preferable.

  The method for applying the non-crosslinked resin particle dispersion on the substrate is not particularly limited. Examples thereof include various methods such as spray coating, spin coating, roll coating, bar coating, slit die coating, and ink jet coating.

  The coating film obtained by applying the non-crosslinked resin particle dispersion on the substrate is dried to obtain a non-crosslinked resin particle layer. The drying temperature may be a temperature at which the shape of the non-crosslinked resin particles is maintained and the non-crosslinked resin particles are bound to each other (for example, 100 ° C.).

  Next, a polyimide precursor solution prepared in advance is impregnated between the non-crosslinked resin particles of the non-crosslinked resin particle layer formed above, and a coating film containing the polyimide precursor solution and the non-crosslinked resin particles is formed. Form. And a coating film is dried and the coating film containing a polyimide precursor and a non-crosslinked resin particle is formed.

The method for impregnating the polyimide precursor solution is not particularly limited. For example, a method in which a substrate on which a non-crosslinked resin particle layer is formed is immersed in a polyimide precursor solution, or a polyimide precursor solution is applied on a non-crosslinked resin particle layer formed on a substrate to form a non-crosslinked resin particle layer. Examples include a method of impregnating between particles.
Examples of the method for applying the polyimide precursor solution on the non-crosslinked resin particle layer formed on the substrate include spray coating, spin coating, roll coating, bar coating, slit die coating, and inkjet coating. And various methods. In addition, in order to impregnate the polyimide precursor solution between the non-crosslinked resin particles forming the non-crosslinked resin particle layer, after applying the polyimide precursor solution from above the non-crosslinked resin particle layer, the pressure is reduced and non-crosslinked Adopting a vacuum impregnation filling method in which the polyimide precursor solution is filled between the resin particles is preferable because the polyimide precursor solution is efficiently impregnated into the voids between the non-crosslinked resin particles.

In addition, as a method of forming the coating film containing a polyimide precursor solution and a non-crosslinked resin particle, it is not restricted to said method.
For example, the following method is specifically mentioned. First, a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved in an aqueous solvent is prepared. Next, this polyimide precursor solution and non-crosslinked resin particles that do not dissolve in the polyimide precursor solution are mixed together to obtain a polyimide precursor solution in which the non-crosslinked resin particles are dispersed (hereinafter referred to as “non-crosslinked resin particle-dispersed polyimide precursor”). Also referred to as “solution”). And this non-crosslinked resin particle-dispersed polyimide precursor solution is apply | coated on a board | substrate, and the coating film containing a polyimide precursor solution and a non-crosslinked resin particle is formed. The non-crosslinked resin particles in the coating film are distributed in a state where aggregation is suppressed (see FIG. 3A). Then, this coating film is dried and the coating film containing a polyimide precursor and a non-crosslinked resin particle is formed on a board | substrate.

  It does not specifically limit as a method of producing said non-crosslinked resin particle dispersion | distribution polyimide precursor solution. Examples thereof include a method of mixing a polyimide precursor solution and dry non-crosslinked resin particles, a method of mixing a polyimide precursor solution and a dispersion in which non-crosslinked resin particles are previously dispersed in an aqueous solvent, and the like. As the dispersion in which the non-crosslinked resin particles are previously dispersed in the aqueous solvent, a dispersion of non-crosslinked resin particles in which the non-crosslinked resin particles are previously dispersed in the aqueous solvent may be prepared. A commercially available dispersion liquid dispersed in an aqueous solvent may be prepared. When preparing a dispersion of non-crosslinked resin particles dispersed in advance, for example, the dispersibility of the non-crosslinked resin particles may be enhanced by at least one of an ionic surfactant and a nonionic surfactant. .

  In the polyimide precursor solution in which the non-crosslinked resin particles are dispersed, the ratio of the non-crosslinked resin particles is a mass ratio when the solid content of the polyimide precursor solution is 100, and the polyimide precursor solution solid content: non Crosslinked resin particles = 100: 20 or more and 100: 200 or less are preferable. The range is preferably from 100: 25 to 100: 180, and more preferably from 100: 30 to 100: 150.

  The method for applying the non-crosslinked resin particle-dispersed polyimide precursor solution on the substrate is not particularly limited. Examples thereof include various methods such as spray coating, spin coating, roll coating, bar coating, slit die coating, and ink jet coating.

  The coating amount of the polyimide precursor solution for obtaining the coating film containing the polyimide precursor solution obtained by the above method and the non-crosslinked resin particles is that the porosity of the porous polyimide film is increased. The amount is preferably such that the non-crosslinked resin particles are exposed from the surface of the membrane. For example, when the polyimide precursor solution is impregnated between the non-crosslinked resin particles on which the non-crosslinked resin particle layer is formed, the polyimide precursor solution is impregnated so as to be less than the thickness of the non-crosslinked resin particle layer. Is good.

  In addition, when forming a non-crosslinked resin particle-dispersed polyimide precursor solution on a substrate, it is preferable to add and form an amount of resin particles in which the non-crosslinked resin particles are exposed from the surface of the coating film.

  And after forming the coating film containing the polyimide precursor solution and non-crosslinked resin particle obtained by the above method, it dries, and the coating film containing a polyimide precursor and a non-crosslinked resin particle is formed. Specifically, the coating film containing the polyimide precursor solution and the non-crosslinked resin particles is dried by a method such as heat drying, natural drying, or vacuum drying to form a coating film. More specifically, the coating film is dried so that the solvent remaining in the coating film is 50% or less, preferably 30% or less, based on the solid content of the coating film, thereby forming the coating film. This coating is in a state where the polyimide precursor can be dissolved in water.

  The coating film may be formed in such an amount that the non-crosslinked resin particles are buried in the coating film. In this case, in the first step, after obtaining the coating film, in the process of drying to form the coating film, a process of exposing the non-crosslinked resin particles is performed to make the non-crosslinked resin particles exposed. May be. By performing the treatment for exposing the non-crosslinked resin particles, the porosity of the porous polyimide film is increased.

Specific examples of the treatment for exposing the non-crosslinked resin particles include the following methods.
When the non-crosslinked resin particle layer is impregnated with the polyimide precursor solution and the coating film is formed so that the non-crosslinked resin particle layer is buried, the area is equal to or greater than the thickness of the non-crosslinked resin particle layer. There is a polyimide precursor solution (see FIG. 1B).

  After obtaining the coating film containing the polyimide precursor solution and the non-crosslinked resin particles, in the process of drying the coating film and forming the film containing the polyimide precursor and the non-crosslinked resin particles, as described above, The polyimide precursor can be dissolved in water. When the coating is in this state, the non-crosslinked resin particles can be exposed, for example, by wiping or immersing in water. Specifically, the thickness of the non-crosslinked resin particle layer is obtained by, for example, performing a treatment for exposing the non-crosslinked resin particle layer by wiping with a polyimide precursor solution existing in a region greater than the thickness of the non-crosslinked resin particle layer. The polyimide precursor solution present in the above region is removed. Then, the non-crosslinked resin particles present in the upper region of the non-crosslinked resin particle layer (that is, the region on the side away from the substrate of the non-crosslinked resin particle layer) are exposed from the surface of the coating (FIG. 1C). reference).

  In the case of forming a film on the substrate using the non-crosslinked resin particle-dispersed polyimide precursor solution, the non-crosslinked resin particles embedded in the film are also formed when the film in which the non-crosslinked resin particles are embedded is formed. As the exposure process, the same process as the process of exposing the non-crosslinked resin particles described above may be employed.

(Second step)
The second step is a step of heating the coating containing the polyimide precursor and non-crosslinked resin particles obtained in the first step to imidize the polyimide precursor to form a polyimide film. And the process which removes a non-crosslinked resin particle is included in the 2nd process. A porous polyimide film is obtained through the treatment for removing the non-crosslinked resin particles.

  In the second step, the step of forming the polyimide film is specifically performed by heating the film containing the polyimide precursor and non-crosslinked resin particles obtained in the first step to advance imidization, and further heating. Thus, a polyimide film is formed. In addition, as imidization proceeds and the imidization rate increases, it becomes difficult to dissolve in an organic solvent.

And in the 2nd process, the process which removes a non-crosslinked resin particle is performed. The non-crosslinked resin particles may be removed in the process of imidizing the polyimide precursor by heating the coating, or may be removed from the polyimide film after imidization is completed (after imidization).
In this embodiment, the process of imidizing the polyimide precursor refers to heating the film containing the polyimide precursor and non-crosslinked resin particles obtained in the first step to advance imidization and imidize. The process which will be in the state before becoming a polyimide film after completion of is shown.

  Specifically, the coating film exposed to the non-crosslinked resin particles obtained in the first step is heated to imidize the polyimide precursor (hereinafter referred to as “polyimide film”). In some cases, the non-crosslinked resin particles are removed. Or you may remove a non-crosslinked resin particle from the polyimide film after imidation is completed. And the porous polyimide film from which the non-crosslinked resin particle was removed is obtained (refer FIG.1 (D)).

  In the process of removing the non-crosslinked resin particles, the non-crosslinked resin component of the non-crosslinked resin particles is contained in the porous polyimide film as a non-crosslinked resin other than the polyimide resin. Although not shown, the porous polyimide film contains a non-crosslinked resin other than the polyimide resin.

  The treatment for removing the non-crosslinked resin particles is in the process of imidizing the polyimide precursor in terms of the removability of the non-crosslinked resin particles, and the imidation ratio of the polyimide precursor in the polyimide film is 30% or more. It is preferable to carry out. When the imidization ratio is 30% or more, it becomes difficult to dissolve in an organic solvent.

  The treatment for removing the non-crosslinked resin particles is not particularly limited as long as the porous polyimide film is obtained so that the non-crosslinked resin is contained. For example, a method of removing the non-crosslinked resin particles by heating, a method of removing the non-crosslinked resin particles with an organic solvent that dissolves the non-crosslinked resin particles, a method of removing the non-crosslinked resin particles by decomposition with a laser or the like, and the like can be mentioned. Among these, the method of removing the non-crosslinked resin particles with an organic solvent is preferable from the viewpoint of suppressing the occurrence of cracks in the porous polyimide film.

  For example, in the method of removing by heating, decomposition gas due to heating may be generated depending on the type of non-crosslinked resin particles. Due to the decomposition gas, the porous polyimide film may be broken or cracked. Therefore, it is preferable to employ a method of removing the non-crosslinked resin particles with an organic solvent that dissolves the non-crosslinked resin particles in terms of suppressing the occurrence of cracks. It is also effective to increase the removal rate by further heating after removing the non-crosslinked resin particles with an organic solvent that dissolves them.

  In addition, when the non-crosslinked resin particles are removed by a method of removing the non-crosslinked resin particles by an organic solvent that dissolves the non-crosslinked resin particles, the non-crosslinked resin component of the non-crosslinked resin particles dissolved in the organic solvent is removed in the process of removing the non-crosslinked resin particles. In some cases, it may penetrate into the polyimide film. Therefore, by adopting this method, the obtained porous polyimide film can positively contain a non-crosslinked resin other than the polyimide resin. From the viewpoint of containing a non-crosslinked resin other than the polyimide resin, it is preferable to employ a method of removing the non-crosslinked resin particles with an organic solvent that dissolves the non-crosslinked resin particles. Further, the removal of the non-crosslinked resin particles by this method is preferably performed on the coating (polyimide film) in the process of imidizing the polyimide precursor in that a non-crosslinked resin other than the polyimide resin is contained. When the non-crosslinked resin particles are dissolved in the state of the polyimide film by a solvent that dissolves the non-crosslinked resin particles, the polyimide film may be more easily penetrated.

  As a method of removing the non-crosslinked resin particles with an organic solvent that dissolves the non-crosslinked resin particles, for example, a method of bringing the non-crosslinked resin particles into contact with the organic solvent in which the non-crosslinked resin particles are dissolved (for example, immersing in a solvent) and dissolving and removing the non-crosslinked resin particles Is mentioned. In this state, it is preferable to immerse in a solvent because the dissolution efficiency of the non-crosslinked resin particles is increased.

As an organic solvent for dissolving the non-crosslinked resin particles for removing the non-crosslinked resin particles, as long as the non-crosslinked resin particles are soluble, the polyimide film and the polyimide film after imidization are not dissolved. There is no particular limitation. For example, ethers such as tetrahydrofuran; aromatics such as toluene; ketones such as acetone; esters such as ethyl acetate;
Among these, ethers such as tetrahydrofuran are preferable, and tetrahydrofuran is more preferable.
When the aqueous solvent remains when dissolving the non-crosslinked resin particles, the aqueous solvent dissolves in the solvent dissolving the non-crosslinked particles, and the polyimide precursor is precipitated, which is similar to the so-called wet phase conversion method. The amount of the remaining aqueous solvent is 20% by mass or less, preferably 10% by mass or less, after being reduced to 10% by mass or less with respect to the polyimide precursor mass. It is preferable to dissolve and remove the non-crosslinked particles.

  In the second step, the heating method for heating the coating obtained in the first step to advance imidization to obtain a polyimide film is not particularly limited. For example, there is a method of heating in two stages. When heating in two stages, specifically, the following heating conditions are mentioned.

  The first stage heating condition is desirably a temperature at which the shape of the non-crosslinked resin particles is maintained. Specifically, for example, a range from 50 ° C. to 150 ° C. is preferable, and a range from 60 ° C. to 140 ° C. is preferable. The heating time is preferably in the range of 10 minutes to 60 minutes. The heating time may be shorter as the heating temperature is higher.

  Examples of the second stage heating condition include heating at 150 to 400 ° C. (preferably 200 to 390 ° C.) for 20 to 120 minutes. By setting the heating conditions within this range, the imidization reaction further proceeds and a polyimide film can be formed. In the heating reaction, before reaching the final temperature of heating, it is preferable to heat by gradually increasing the temperature stepwise or at a constant rate.

  The heating conditions are not limited to the above two-stage heating method, and for example, a method of heating in one stage may be adopted. In the case of the method of heating in one stage, for example, imidization may be completed only by the heating conditions shown in the second stage.

  In the case where the treatment for exposing the non-crosslinked resin particles is not performed in the first step, the treatment for exposing the non-crosslinked resin particles is performed in the second step in order to increase the porosity. It is preferable to be in a state where is exposed. In the second step, the treatment for exposing the non-crosslinked resin particles is preferably performed in the process of imidizing the polyimide precursor, or after the imidization and before the treatment for removing the non-crosslinked resin particles.

  For example, in the first step, a non-crosslinked resin particle layer is formed on the substrate (see FIG. 2A), and a polyimide precursor solution is impregnated between the non-crosslinked resin particles of the non-crosslinked resin particle layer. A coating film in which the crosslinked resin particles are buried is formed (see FIG. 2B). Next, in the process of drying the coating film to form the coating film, a coating film containing the polyimide precursor and the non-crosslinked resin particles is formed without performing the treatment for exposing the non-crosslinked resin particles. The film formed by this method forms a film in which the non-crosslinked resin particle layer is buried. This coating is heated to remove the non-crosslinked resin particles, and before the removal treatment of the non-crosslinked resin particles, the process of imidizing the polyimide precursor, or the polyimide film after imidization is completed (after imidization) A process for exposing the particles is performed.

In the second step, the treatment for exposing the non-crosslinked resin particles may be performed, for example, when the polyimide film is in the following state.
When the imidation ratio of the polyimide precursor in the polyimide film is less than 15% (that is, the state in which the polyimide film can be dissolved in water), when the treatment for exposing the non-crosslinked resin particles is performed, the polyimide film is buried in the polyimide film. Examples of the process for exposing the non-crosslinked resin particles that are exposed include a wiping process and a process of immersing in water.

Moreover, when the imidation ratio of the polyimide precursor in the polyimide film is 15% or more (that is, in a state in which it is difficult to dissolve in an organic solvent), and when the polyimide film has been imidized, it is non-crosslinked. In the case of performing the treatment for exposing the resin particles, a method of exposing the non-crosslinked resin particles by mechanical cutting with a tool such as a sandpaper, a method of exposing the non-crosslinked resin particles by decomposition with a laser or the like can be mentioned. It is done.
For example, when mechanically cutting, the non-crosslinked resin present in the upper region of the non-crosslinked resin particle layer buried in the polyimide film (that is, the region on the side away from the substrate of the non-crosslinked resin particle layer). Part of the particles is cut together with the polyimide film present on the upper part of the non-crosslinked resin particles, and the cut non-crosslinked resin particles are exposed from the surface of the polyimide film (see FIG. 2C).

  Thereafter, the non-crosslinked resin particles are removed from the polyimide film from which the non-crosslinked resin particles are exposed by the above-described removal treatment of the non-crosslinked resin particles. And the porous polyimide film from which the non-crosslinked resin particle was removed is obtained (refer FIG.2 (D)).

  In addition, when forming a film on a substrate using a non-crosslinked resin particle-dispersed polyimide precursor solution, the non-crosslinked resin particle-dispersed polyimide precursor solution is applied on the substrate to form a coating film in which the non-crosslinked resin particles are buried. (See FIG. 3A). In the process of drying the coating film to form a coating film, the coating film including the polyimide precursor and the non-crosslinking resin particles is formed without performing the treatment for exposing the non-crosslinking resin particles. Is formed. And the film (polyimide film) in the process of imidizing by heating to this film is in a state where the non-crosslinked resin particle layer is buried. In order to increase the open area ratio, the treatment for exposing the non-crosslinked resin particles performed in the second step can be the same as the treatment for exposing the non-crosslinked resin particles described above. And it cuts with the polyimide film which exists on the upper part of a non-crosslinked resin particle, and a non-crosslinked resin particle is exposed from the surface of a polyimide film (refer to Drawing 3 (B)).

  Thereafter, the non-crosslinked resin particles are removed from the polyimide film from which the non-crosslinked resin particles are exposed by the above-described removal treatment of the non-crosslinked resin particles. And the porous polyimide film from which the non-crosslinked resin particle was removed is obtained (refer FIG.3 (C)).

  In the second step, the substrate for forming the coating used in the first step may be peeled off when it becomes a dry coating, and the polyimide precursor in the polyimide film is organic. It may be peeled off when it is difficult to dissolve in a solvent, or it may be peeled off when the film has been imidized.

  Through the above steps, a porous polyimide film containing a polyimide resin and a non-crosslinked resin other than the polyimide resin is obtained. The porous polyimide film may be post-processed depending on the purpose of use.

[Polyimide precursor solution]
The polyimide precursor solution is not particularly limited as long as a porous polyimide film containing non-crosslinked resin other than polyimide resin is obtained. A polyimide precursor solution in which a polyimide precursor is dissolved in an aqueous solvent is preferable in terms of suppressing the occurrence of cracks.

  Hereinafter, each component of the polyimide precursor solution for obtaining the porous polyimide film which concerns on this embodiment is demonstrated. In addition, the polyimide precursor solution in which the polyimide precursor and the organic amine compound are dissolved in the aqueous solvent will be described as an example.

(Polyimide precursor)
A polyimide precursor is resin (polyamic acid) which has a repeating unit represented by general formula (I).

(In general formula (I), A represents a tetravalent organic group, and B represents a divalent organic group.)

Here, in the general formula (I), the tetravalent organic group represented by A is a residue obtained by removing four carboxyl groups from a tetracarboxylic dianhydride as a raw material.
On the other hand, the divalent organic group represented by B is a residue obtained by removing two amino groups from a diamine compound as a raw material.

  That is, the polyimide precursor having the repeating unit represented by the general formula (I) is a polymer of tetracarboxylic dianhydride and a diamine compound.

  The tetracarboxylic dianhydride includes both aromatic and aliphatic compounds, but is preferably an aromatic compound. That is, in the general formula (I), the tetravalent organic group represented by A is preferably an aromatic organic group.

  Examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, and 3,3 ′, 4,4′-biphenyl. Sulfonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3 ′, 4,4′- Biphenyl ether tetracarboxylic dianhydride, 3,3 ′, 4,4′-dimethyldiphenylsilane tetracarboxylic dianhydride, 3,3 ′, 4,4′-tetraphenylsilane tetracarboxylic dianhydride, 1 , 2,3,4-furantetracarboxylic dianhydride, 4,4′-bis (3,4-dicarboxyphenoxy) diphenyl sulfide dianhydride, 4,4′-bis (3,4-dicarboxyl) Noxi) diphenylsulfone dianhydride, 4,4′-bis (3,4-dicarboxyphenoxy) diphenylpropane dianhydride, 3,3 ′, 4,4′-perfluoroisopropylidenediphthalic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, bis (phthalic acid) phenylphosphine oxide dianhydride, p- Phenylene-bis (triphenylphthalic acid) dianhydride, m-phenylene-bis (triphenylphthalic acid) dianhydride, bis (triphenylphthalic acid) -4,4′-diphenyl ether dianhydride, bis (triphenyl) Phthalic acid) -4,4'-diphenylmethane dianhydride.

  Examples of the aliphatic tetracarboxylic dianhydride include butanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4. -Cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic acid dianhydride, 3,5,6-tricarboxynorbonane 2-acetic acid dianhydride, 2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, 5- (2,5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene-1,2-dicarboxylic acid Aliphatic or alicyclic tetracarboxylic dianhydrides such as acid dianhydrides, bicyclo [2,2,2] -oct-7-ene-2,3,5,6-tetracarboxylic dianhydrides; , 3,3a, 4,5,9b-hexahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione, 1,3,3a, 4,5 9b-Hexahydro-5-methyl-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione, 1,3,3a, 4,5 Aliphatic tetracarboxylic acids having an aromatic ring such as 9b-hexahydro-8-methyl-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione A dianhydride etc. are mentioned.

  Among these, the tetracarboxylic dianhydride is preferably an aromatic tetracarboxylic dianhydride, specifically, for example, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyl. Tetracarboxylic dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyl ether tetracarboxylic dianhydride, 3,3 ′, 4 , 4′-benzophenonetetracarboxylic dianhydride is preferable, and pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4 ′ -Benzophenone tetracarboxylic dianhydride is good, especially 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride.

In addition, tetracarboxylic dianhydride may be used individually by 1 type, and may be used together in combination of 2 or more types.
In addition, when two or more types are used in combination, aromatic tetracarboxylic dianhydride or aliphatic tetracarboxylic dianhydride and aliphatic tetracarboxylic dianhydride may be used in combination. You may combine things.

  On the other hand, a diamine compound is a diamine compound having two amino groups in the molecular structure. Examples of diamine compounds include aromatic and aliphatic compounds, but aromatic compounds are preferred. That is, in the general formula (I), the divalent organic group represented by B is preferably an aromatic organic group.

Examples of the diamine compound include p-phenylenediamine, m-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylethane, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl sulfide. 4,4′-diaminodiphenylsulfone, 1,5-diaminonaphthalene, 3,3-dimethyl-4,4′-diaminobiphenyl, 5-amino-1- (4′-aminophenyl) -1,3,3 -Trimethylindane, 6-amino-1- (4'-aminophenyl) -1,3,3-trimethylindane, 4,4'-diaminobenzanilide, 3,5-diamino-3'-trifluoromethylbenzanilide 3,5-diamino-4′-trifluoromethylbenzanilide, 3,4′-diaminodiphenyl ether, , 7-diaminofluorene, 2,2-bis (4-aminophenyl) hexafluoropropane, 4,4′-methylene-bis (2-chloroaniline), 2,2 ′, 5,5′-tetrachloro-4 , 4'-diaminobiphenyl, 2,2'-dichloro-4,4'-diamino-5,5'-dimethoxybiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 4,4'-diamino -2,2'-bis (trifluoromethyl) biphenyl, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoro Propane, 1,4-bis (4-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) -biphenyl, 1,3′-bis (4-aminophenoxy) benzene, 9,9-bi (4-aminophenyl) fluorene, 4,4 ′-(p-phenyleneisopropylidene) bisaniline, 4,4 ′-(m-phenyleneisopropylidene) bisaniline, 2,2′-bis [4- (4-amino- Aromatic diamines such as 2-trifluoromethylphenoxy) phenyl] hexafluoropropane, 4,4′-bis [4- (4-amino-2-trifluoromethyl) phenoxy] -octafluorobiphenyl; diaminotetraphenylthiophene, etc. An aromatic diamine having two amino groups bonded to the aromatic ring and a hetero atom other than the nitrogen atom of the amino group; 1,1-metaxylylenediamine, 1,3-propanediamine, tetramethylenediamine, penta Methylenediamine, octamethylenediamine, nonamethylenediamine, 4,4-diaminohe Data diamine, 1,4-diaminocyclohexane, isophorone diamine, tetrahydrodicyclopentadiene cyclopentadienylide diamine, hexahydro-4,7-meth Noin mite range diamine, tricyclo [6,2,1,0 ^2.7] Examples thereof include aliphatic diamines such as undecylenedimethyl diamine and 4,4′-methylene bis (cyclohexylamine), and alicyclic diamines.

  Among these, as the diamine compound, an aromatic diamine compound is good, and specifically, for example, p-phenylenediamine, m-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl sulfide, and 4,4′-diaminodiphenyl sulfone are preferable, and 4,4′-diaminodiphenyl ether and p-phenylenediamine are particularly preferable.

  In addition, a diamine compound may be used individually by 1 type, and may be used together in combination of 2 or more types. Moreover, when using together and using 2 or more types, you may use together an aromatic diamine compound or an aliphatic diamine compound, respectively, or may combine an aromatic diamine compound and an aliphatic diamine compound.

The number average molecular weight of the polyimide precursor is preferably from 1,000 to 150,000, more preferably from 5,000 to 130,000, and even more preferably from 10,000 to 100,000.
When the number average molecular weight of the polyimide precursor is within the above range, a decrease in the solubility of the polyimide precursor in the solvent is suppressed, and film forming properties are easily secured.

The number average molecular weight of the polyimide precursor is measured by a gel permeation chromatography (GPC) method under the following measurement conditions.
Column: Tosoh TSKgel α-M (7.8 mm ID × 30 cm)
Eluent: DMF (dimethylformamide) / 30 mM LiBr / 60 mM phosphoric acidFlow rate: 0.6 mL / min
・ Injection volume: 60 μL
・ Detector: RI (differential refractive index detector)

  The content (concentration) of the polyimide precursor may be 0.1% by mass or more and 40% by mass or less, preferably 0.5% by mass or more and 25% by mass or less, based on the total polyimide precursor solution. Preferably they are 1 mass% or more and 20 mass% or less.

(Organic amine compound)
An organic amine compound is a compound that functions as an imidization accelerator while amine-treating a polyimide precursor (its carboxyl group) to increase its solubility in an aqueous solvent. Specifically, the organic amine compound is preferably an amine compound having a molecular weight of 170 or less. The organic amine compound may be a compound excluding a diamine compound that is a raw material for the polyimide precursor.
The organic amine compound is preferably a water-soluble compound. Water-soluble means that the target substance dissolves 1% by mass or more in water at 25 ° C.

Examples of organic amine compounds include primary amine compounds, secondary amine compounds, and tertiary amine compounds.
Among these, as the organic amine compound, at least one selected from a secondary amine compound and a tertiary amine compound (particularly a tertiary amine compound) is preferable. When a tertiary amine compound or a secondary amine compound is applied as the organic amine compound (particularly a tertiary amine compound), the solubility of the polyimide precursor in the solvent is likely to be increased, and the film forming property is easily improved. Storage stability of the polyimide precursor solution is easily improved.

  Moreover, as an organic amine compound, the polyvalent amine compound more than bivalence other than a monovalent amine compound is also mentioned. When a polyvalent amine compound having two or more valences is applied, a pseudo-crosslinked structure is easily formed between the molecules of the polyimide precursor, and the storage stability of the polyimide precursor solution is easily improved.

Examples of the primary amine compound include methylamine, ethylamine, n-propylamine, isopropylamine, 2-ethanolamine, 2-amino-2-methyl-1-propanol, and the like.
Examples of the secondary amine compound include dimethylamine, 2- (methylamino) ethanol, 2- (ethylamino) ethanol, morpholine, and the like.
Examples of the tertiary amine compound include 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, methylmorpholine, ethylmorpholine, 1,2-dimethylimidazole, and 2-ethyl-4. -Methylimidazole etc. are mentioned.

  Here, as the organic amine compound, an amine compound having a heterocyclic structure containing nitrogen (particularly, a tertiary amine compound) is also preferable from the viewpoint of film forming properties. Examples of amine compounds having a heterocyclic structure containing nitrogen (hereinafter referred to as “nitrogen-containing heterocyclic amine compounds”) include, for example, isoquinolines (amine compounds having an isoquinoline skeleton) and pyridines (amine compounds having a pyridine skeleton). ), Pyrimidines (amine compounds having pyrimidine skeleton), pyrazines (amine compounds having pyrazine skeleton), piperazines (amine compounds having piperazine skeleton), triazines (amine compounds having triazine skeleton), imidazoles (imidazole) Amine compounds having a skeleton), morpholines (amine compounds having a morpholine skeleton), polyaniline, polypyridine, polyamine, and the like.

  The nitrogen-containing heterocyclic amine compound is preferably at least one selected from the group consisting of morpholines, pyridines, and imidazoles from the viewpoint of film forming properties, and more preferably from N-methylmorpholine, pyridine, and picoline. More preferably, it is at least one selected from the group consisting of:

  Among these, the organic amine compound is preferably a compound having a boiling point of 60 ° C. or higher (preferably 60 ° C. or higher and 200 ° C. or lower, more preferably 70 ° C. or higher and 150 ° C. or lower). When the boiling point of the organic amine compound is 60 ° C. or higher, the organic amine compound is prevented from volatilizing from the polyimide precursor solution during storage, and the solubility of the polyimide precursor in the solvent is easily suppressed.

The organic amine compound may be contained in an amount of 50 mol% to 500 mol%, preferably 80 mol% to 250 mol%, based on the carboxyl group (—COOH) of the polyimide precursor in the polyimide precursor solution. More preferably, it is contained at 90 mol% or more and 200 mol% or less.
When the content of the organic amine compound is in the above range, the solubility of the polyimide precursor in the solvent is likely to increase, and the film forming property is easily improved. Moreover, it becomes easy to improve the storage stability of the polyimide precursor solution.

  Said organic amine compound may be used individually by 1 type, and may be used together 2 or more types.

(Aqueous solvent)
The aqueous solvent is an aqueous solvent containing water. Specifically, the aqueous solvent is preferably a solvent containing 50% by mass or more of water with respect to the total aqueous solvent. Examples of water include distilled water, ion exchange water, ultrafiltration water, and pure water.

  The content of water is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, and still more preferably 80% by mass or more and 100% by mass or less with respect to the total aqueous solvent.

  When the aqueous solvent includes a solvent other than water, examples of the solvent other than water include a water-soluble organic solvent and an aprotic polar solvent. As the solvent other than water, a water-soluble organic solvent is preferable from the viewpoints of transparency and mechanical strength of the polyimide molded body. In particular, from the viewpoint of improving various properties of the polyimide molded product such as heat resistance, electrical properties and solvent resistance in addition to transparency and mechanical strength, the aqueous solvent does not contain an aprotic polar solvent or contains a small amount. (For example, 40% by mass or less, preferably 30% by mass or less with respect to the total aqueous solvent). Here, water-soluble means that the target substance dissolves 1% by mass or more with respect to water at 25 ° C.

  Although the said water-soluble organic solvent may be used individually by 1 type, you may use 2 or more types together.

  The water-soluble ether solvent is a water-soluble solvent having an ether bond in one molecule. Examples of the water-soluble ether solvent include tetrahydrofuran (THF), dioxane, trioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and the like. Among these, tetrahydrofuran and dioxane are preferable as the water-soluble ether solvent.

  The water-soluble ketone solvent is a water-soluble solvent having a ketone group in one molecule. Examples of the water-soluble ketone solvent include acetone, methyl ethyl ketone, and cyclohexanone. Among these, acetone is preferable as the water-soluble ketone solvent.

  The water-soluble alcohol solvent is a water-soluble solvent having an alcoholic hydroxyl group in one molecule. Examples of the water-soluble alcohol solvent include methanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, ethylene glycol monoalkyl ether, propylene glycol, propylene glycol monoalkyl ether, diethylene glycol, and diethylene glycol. Monoalkyl ether, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-butene- Examples include 1,4-diol, 2-methyl-2,4-pentanediol, glycerin, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 1,2,6-hexanetriol and the like. Among these, as the water-soluble alcohol solvent, methanol, ethanol, 2-propanol, ethylene glycol, monoalkyl ether of ethylene glycol, propylene glycol, monoalkyl ether of propylene glycol, diethylene glycol, and monoalkyl ether of diethylene glycol are preferable.

  When an aprotic polar solvent other than water is contained as the aqueous solvent, the aprotic polar solvent used in combination is a solvent having a boiling point of 150 ° C. or higher and 300 ° C. or lower and a dipole moment of 3.0D or higher and 5.0D or lower. is there. Specific examples of the aprotic polar solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), Hexamethylene phosphoramide (HMPA), N-methylcaprolactam, N-acetyl-2-pyrrolidone, N, N-dimethylimidazolidinone (DMI), N, N′-dimethylpropyleneurea, tetramethylurea, trimethyl phosphate And triethyl phosphate.

  In addition, when a solvent other than water is contained as the aqueous solvent, the solvent used in combination may have a boiling point of 270 ° C. or lower, preferably 60 ° C. or higher and 250 ° C. or lower, more preferably 80 ° C. or higher and 230 ° C. or lower. is there. When the boiling point of the solvent used in combination is in the above range, it is difficult for a solvent other than water to remain in the polyimide molded body, and a polyimide molded body having high mechanical strength is easily obtained.

  Here, the range in which the polyimide precursor is dissolved in the solvent is controlled by the water content and the type and amount of the organic amine compound. In a range where the water content is low, the polyimide precursor is easily dissolved in a region where the content of the organic amine compound is low. On the contrary, in the range where the content of water is high, the polyimide precursor is easily dissolved in a region where the content of the organic amine compound is large. Further, when the organic amine compound has high hydrophilicity such as a hydroxyl group, the polyimide precursor is easily dissolved in a region where the water content is high.

  In addition, a polyimide precursor synthesized with an organic solvent such as an aprotic polar solvent (for example, N-methylpyrrolidone (NMP)) is added to a poor solvent such as water or alcohol, precipitated, and separated. It may be a precursor.

(Other additives)
In the method for producing a porous polyimide film according to the present embodiment, the polyimide precursor solution may include a catalyst for promoting imidization reaction, a leveling material for improving film forming quality, and the like.
As the catalyst for promoting the imidization reaction, a dehydrating agent such as an acid anhydride, an acid catalyst such as a phenol derivative, a sulfonic acid derivative, or a benzoic acid derivative may be used.

Further, depending on the purpose of use of the porous polyimide film, for example, a conductive material (conductivity (for example, volume resistivity less than 10 ⁷ Ω · cm) or It may contain semiconductivity (for example, volume resistivity 10 ⁷ Ω · cm or more and 10 ¹³ Ω · cm or less).
Examples of the conductive agent include carbon black (for example, acidic carbon black having a pH of 5.0 or less); metal (for example, aluminum or nickel); metal oxide (for example, yttrium oxide, tin oxide); ion conductive material (for example, titanium) Acid potassium, LiCl, etc.); These conductive materials may be used alone or in combination of two or more.

Moreover, the polyimide precursor solution may contain inorganic particles added for improving the mechanical strength depending on the purpose of use of the porous polyimide film. Examples of the inorganic particles include particulate materials such as silica powder, alumina powder, barium sulfate powder, titanium oxide powder, mica, and talc. Moreover, LiCoO _2, LiMn ₂ O or the like may also contain used as an electrode of a lithium ion battery.

(Method for producing polyimide precursor solution)
Although it does not specifically limit as a manufacturing method of the polyimide precursor solution which concerns on this embodiment, For example, the manufacturing method shown below is mentioned.

As an example, there is a method in which a tetracarboxylic dianhydride and a diamine compound are polymerized in an aqueous solvent in the presence of an organic amine compound to produce a resin (polyimide precursor) to obtain a polyimide precursor solution. .
According to this method, since the aqueous solvent is applied, the productivity is high and the polyimide precursor solution is produced in one step, which is advantageous in terms of simplification of the process.

  As another example, a resin (polyimide precursor) is obtained by polymerizing tetracarboxylic dianhydride and a diamine compound in an organic solvent such as an aprotic polar solvent (for example, N-methylpyrrolidone (NMP)). Then, it is poured into an aqueous solvent such as water or alcohol to precipitate a resin (polyimide precursor). Thereafter, a method of obtaining a polyimide precursor solution by dissolving a polyimide precursor and an organic amine compound in an aqueous solvent can be mentioned.

  In addition, although the example of the polyimide precursor solution in which the polyimide precursor and the organic amine compound were melt | dissolved in the aqueous solvent was given, it does not restrict to this. For example, a polyimide precursor solution in which the organic amine compound is not dissolved can be mentioned. Specifically, an aqueous mixed solvent selected from a water-soluble ether solvent, a water-soluble ketone solvent, a water-soluble alcohol solvent, and water (for example, a water-soluble ether solvent and water, or a water-soluble ketone solvent and water, etc. In combination with a water-soluble alcohol solvent, etc.) to form a resin (polyimide precursor) by polymerizing tetracarboxylic dianhydride and a diamine compound to obtain a polyimide precursor solution. .

  Next, the porous polyimide film according to this embodiment will be described.

(Content of non-crosslinked resin other than polyimide resin)
The presence state of the non-crosslinked resin other than the polyimide resin contained in the porous polyimide film of the present embodiment is not particularly limited. For example, it may be present in at least one of the inside of the porous polyimide film and the surface of the porous polyimide film (including the pore surface of the porous polyimide film).

  As content of non-crosslinked resin other than a polyimide resin, it is desirable that it is 0.1 mass% or more and 5 mass% or less at the point which suppresses generation | occurrence | production of a crack. The content is more preferably 0.2% by mass or more and 4.8% by mass or less, and further preferably 0.3% by mass or more and 4.6% by mass or less. In addition, the smoothness of a porous polyimide film can improve by containing non-crosslinked resin other than a polyimide resin in this range.

  The amount of the non-crosslinked resin other than the polyimide resin contained in the porous polyimide film can be measured by, for example, pyrolysis gas chromatography mass spectrometry (GC-MS). The ratio of the non-crosslinked resin other than the polyimide resin can be calculated from the peak corresponding to the non-crosslinked resin other than the polyimide resin and the area thereof. Moreover, being a non-crosslinked resin means that polyfunctional components other than the polyimide resin are not detected in the obtained chromatogram. It is also possible to analyze the non-crosslinked resin component by liquid chromatography (HPLC), nuclear magnetic resonance (NMR) or the like after hydrolysis of the polyimide resin.

(Characteristics of porous polyimide film)
In the porous polyimide film of this embodiment, the shape of the pores is spherical. In the present embodiment, the shape of the pores is “spherical” includes both spherical shapes and substantially spherical shapes (shapes close to spherical shapes). Specifically, it means that the ratio of pores having a major axis / minor axis ratio (major axis / minor axis) of 1 to 1.5 is 90% or more. The greater the presence ratio of the holes, the higher the ratio of spherical holes. The pores having a major axis / minor axis ratio (major axis / minor axis) of 1 or more and 1.5 or less are preferably 93% or more and 100% or less, and more preferably 95% or more and 100% or less. Further, the closer the ratio of the major axis to the minor axis approaches 1, the closer to a perfect sphere.
In addition, when the porous polyimide film of the present embodiment is applied to, for example, a battery separator of a lithium ion battery, the occurrence of ion flow turbulence is suppressed, so that formation of lithium dendrite is easily suppressed.

  The porous polyimide film of this embodiment is not particularly limited, but the porosity is preferably 30% or more. Moreover, it is preferable that a porosity is 40% or more, and it is more preferable that it is 50% or more. The upper limit of the porosity is not particularly limited, but is preferably in the range of 90% or less.

  In addition, it is preferable that the holes have a shape in which the holes are connected to each other (see FIGS. 1D, 2D, and 3C). The hole diameter of the portion where the holes are connected to each other is preferably, for example, 1/100 or more and 1/2 or less, and preferably 1/50 or more and 1/3 or less of the maximum diameter of the holes. More preferably, it is 1/20 or more and 1/4 or less. Specifically, the average value of the hole diameters of the portions where the holes are connected to each other is preferably 5 nm or more and 1500 nm or less.

  The average value of the pore diameter is not particularly limited, but is preferably in the range of 0.01 μm to 2.5 μm, more preferably in the range of 0.05 μm to 2.0 μm, and more preferably 0.1 μm to 1.5 μm. The following range is preferable, and a range of 0.15 μm to 1.0 μm is more preferable.

In the porous polyimide film of this embodiment, the ratio of the maximum diameter and the minimum diameter of the pores (the ratio of the maximum value and the minimum value of the pore diameter) is 1 or more and 2 or less. Preferably they are 1 or more and 1.9 or less, More preferably, they are 1 or more and 1.8 or less. Of these ranges, a value closer to 1 is more preferable. By being in this range, variation in the hole diameter is suppressed. In addition, when the porous polyimide film of the present embodiment is applied to, for example, a battery separator of a lithium ion battery, the occurrence of ion flow turbulence is suppressed, so that formation of lithium dendrite is easily suppressed.
The “ratio between the maximum diameter and the minimum diameter of the holes” is a ratio represented by a value obtained by dividing the maximum diameter of the holes by the minimum diameter (that is, the maximum value / minimum value of the hole diameter).

  The maximum value, minimum value, average value of the pore diameter, the average value of the pore diameter where the pores are connected to each other, and the major and minor diameters of the pores are observed with a scanning electron microscope (SEM). And a measured value. Specifically, first, a porous polyimide film is cut out to prepare a measurement sample. Then, this measurement sample is observed and measured with image processing software provided as a standard by a VE SEM manufactured by KEYENCE. Observation and measurement are performed for each of the hole portions in the measurement sample cross section, and the average value, minimum diameter, maximum diameter, and arithmetic average diameter are obtained. When the shape of the hole is not circular, the longest part is the diameter. In addition, for each of the above hole portions, the major axis and the minor axis are observed and measured with VE SEM manufactured by Keyence Co., Ltd. using image processing software provided as standard, and the ratio of major axis / minor axis is determined. calculate.

  Although the film thickness of a porous polyimide film is not specifically limited, It is good that they are 15 micrometers or more and 500 micrometers or less.

(Use of porous polyimide film)
Applications for which the porous polyimide film according to this embodiment is applied include, for example, battery separators such as lithium batteries; separators for electrolytic capacitors; electrolyte membranes such as fuel cells; battery electrode materials; gas or liquid separation membranes; Low dielectric constant materials; and the like.

When the porous polyimide film according to the present embodiment is applied to, for example, a battery separator, it is considered that generation of lithium dendrite is suppressed due to an action such as suppression of variations in ion flow distribution of lithium ions. . This is presumed to be because the pore shape and the pore diameter variation of the porous polyimide film of this embodiment are suppressed.
Further, for example, when applied to a battery electrode material, it is considered that the capacity of the battery increases because the chance of contact with the electrolyte increases. This is presumably because the amount of the material such as carbon black for electrodes contained in the porous polyimide film is exposed to the surface of the porous polyimide film on the pore diameter and the surface of the film.
Furthermore, for example, it is also possible to fill the pores of the porous polyimide film with, for example, an ionic gel obtained by gelling a so-called ionic liquid and apply it as an electrolyte membrane. Since the manufacturing method of this embodiment simplifies the process, it is considered that a lower cost electrolyte membrane can be obtained.

  Examples will be described below, but the present invention is not limited to these examples. In the following description, “part” and “%” are all based on mass unless otherwise specified.

[Preparation of polyimide precursor “water” solution (PAA-1)]
A flask equipped with a stir bar, thermometer, and dropping funnel was charged with 900 g of water. To this, p-phenylenediamine (molecular weight 108.14): 27.28 g (252.27 mmol) and methylmorpholine (organic amine compound): 50.00 g (494.32 mmol) were added, and at 20 ° C. Stir for 10 minutes to disperse. Further, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (molecular weight 294.22): 72.72 g (247.16 mmol) was added to this solution, and the reaction temperature was maintained at 20 ° C. The solution was stirred for 24 hours for dissolution and reaction to obtain a polyimide precursor “water” solution (PAA-1).

[Preparation of polyimide precursor “N-methylpyrrolidone” solution (RPAA-1)]
A flask equipped with a stir bar, thermometer and dropping funnel was charged with 900 g of N-methylpyrrolidone. To this, 27.28 g (252.27 mmol) of p-phenylenediamine was added and dispersed by stirring at 20 ° C. for 10 minutes. To this solution was added 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride: 72.72 g (247.16 mmol) and dissolved by stirring for 24 hours while maintaining the reaction temperature at 20 ° C. Then, a reaction was performed to obtain a polyimide precursor “N-methylpyrrolidone” solution (RPAA-1).

[Preparation of polyimide precursor “water / isopropanol” solution (PAA-2)]
500 g of the polyimide precursor “N-methylpyrrolidone” solution (RPAA-1) was added dropwise to 3000 g of water while stirring to precipitate the polyimide precursor. 30 g of this polyimide precursor was added to 243 g of water and 27 g of isopropanol, and further 15 g of methylmorpholine was added and stirred and dissolved to obtain a polyimide precursor “water / isopropanol” solution (PAA-2).

[Preparation of polyimide precursor “water / isopropanol” solution (PAA-3)]
500 g of the polyimide precursor “N-methylpyrrolidone” solution (RPAA-1) was added dropwise to 3000 g of water while stirring to precipitate the polyimide precursor. 30 g of this polyimide precursor is added to 243 g of water and 27 g of isopropanol, and further 15 g of 1,2-dimethylimidazole (DMIz) is added and stirred and dissolved to obtain a polyimide precursor “water / isopropanol” solution (PAA- 3) was obtained.

[Preparation of polyimide precursor “water / N-methylpyrrolidone” solution (PAA-4)]
500 g of the polyimide precursor “N-methylpyrrolidone” solution (RPAA-1) was added dropwise to 3000 g of water while stirring to precipitate the polyimide precursor. 30 g of this polyimide precursor is added to 243 g of water and 27 g of N-methylpyrrolidone, and further, 15 g of 1,2-dimethylimidazole is added and stirred and dissolved to obtain a polyimide precursor “water / N-methylpyrrolidone” solution. (PAA-4) was obtained.

<Example 1>
Non-crosslinked polymethyl methacrylate / styrene copolymer having an average particle size of 0.1 μm (FS-102E: manufactured by Nippon Paint): 10 parts, polyvinyl butyral resin (S-LEC SV-02: manufactured by Sekisui Chemical Co., Ltd.): One part was added to 30 parts of ethanol and stirred on a webblotter to prepare a dispersion solution. This was formed on a glass substrate so that the film thickness after drying was 30 μm, and dried at 90 ° C. for 1 hour to form a non-crosslinked resin particle layer.
After diluting the polyimide precursor “water” solution (PAA-1) 10 times and applying the polyimide precursor “water” solution (PAA-1) on the non-crosslinked resin particle layer, vacuum degassing is performed, The voids between the crosslinked resin particles were impregnated with a polyimide precursor “water” solution (PAA-1). After drying overnight at room temperature (25 ° C., the same applies hereinafter), water was wiped so that the surface of the non-crosslinked resin particle layer was exposed, and excess polyimide precursor on the non-crosslinked resin particle layer was removed. After heating this at 120 ° C. for 1 hour, it was peeled from the glass substrate and immersed in tetrahydrofuran (THF) for 30 minutes to elute non-crosslinked resin particles. After drying, the temperature was raised from room temperature to 380 ° C. at a rate of 10 ° C./min, held at 380 ° C. for 1 hour, and then cooled to room temperature to obtain a porous polyimide film (PIF-1).

<Comparative Example 1>
On the non-crosslinked resin particle layer produced in the same manner as in Example 1, the polyimide precursor “N-methylpyrrolidone” solution (RPAA-1) was diluted 10 times and applied, but the non-crosslinked resin particles were dissolved. Oops. This was heated at 120 ° C. for 1 hour, then peeled off from the glass substrate, and immersed in THF for 1 hour to elute the non-crosslinked resin. After drying, the temperature was raised from room temperature to 380 ° C. at a speed of 10 ° C./min, held at 380 ° C. for 1 hour, and then cooled to room temperature to obtain a porous polyimide film (RPIF-1). However, the pore diameter was in the range of 0.05 μm to 1.01 μm, and the distribution was wide. This is presumably because the non-crosslinked particles were dissolved and the form could not be maintained. In addition, the non-crosslinked resin component derived from non-crosslinked resin particles in the porous polyimide film (RPIF-1) was 0.02%.

<Example 2>
The polyimide precursor “water / isopropanol” solution (PAA-2) was diluted 10 times and applied onto the non-crosslinked resin particle layer produced in the same manner as in Example 1, and the porous polyimide film in the same manner as in Example 1. (PIF-2) was obtained.

<Example 3>
The polyimide precursor “water / isopropanol” solution (PAA-2) was diluted 10 times, and 10 parts of the polyimide precursor was diluted with 10 parts of non-crosslinked polymethyl methacrylate / styrene having an average particle size of 0.1 μm. A copolymer (FS-102E: manufactured by Nippon Paint Co., Ltd.) was added and stirred on a webblotter to prepare a dispersion solution. This was formed on a glass substrate so that the film thickness after drying was about 30 μm, dried at room temperature for 1 hour, then peeled off from the glass substrate and immersed in tetrahydrofuran for 30 minutes. After drying at 90 ° C. for 1 hour, the temperature was raised from 90 ° C. to 380 ° C. at a rate of 10 ° C./minute, held at 380 ° C. for 1 hour, and then cooled to room temperature to form a porous polyimide film (PIF-3). Obtained.

<Example 4>
A porous polyimide film (PIF-4) was obtained in the same manner as in Example 2 except that the polyimide precursor “water / isopropanol” solution (PAA-3) was used.

<Example 5>
Porous polyimide film (PIF-5) in the same manner as in Example 3 except that a polyimide precursor “water / N-methylpyrrolidone” solution (PAA-4) was used and toluene was used to remove non-crosslinked resin particles. Got. Since N-methylpyrrolidone has a high boiling point and cannot be sufficiently removed by drying at room temperature, the pore diameter was larger than that of isopropanol.

<Comparative example 2>
Mono-dispersed spherical silica particles having an average diameter of 550 nm manufactured by Nippon Shokubai Co., Ltd. (true sphere ratio: 1.0, particle size distribution index: 1.20): 30 parts by mass to N-methylpyrrolidone (NMP): 30 parts by mass Distributed. Polyimide precursor “N-methylpyrrolidone” solution (RPAA-1): 100 parts by mass of silica particle dispersion 20 parts by mass was mixed and stirred, and then applied onto a glass plate. This is heated at 120 ° C. for 1 hour, then peeled off from the glass substrate, heated from room temperature to 380 ° C. at a speed of 10 ° C./minute, held at 380 ° C. for 1 hour, then cooled to room temperature and silica -A polyimide composite membrane was obtained. The silica-polyimide composite film was immersed in 10% by mass of hydrogen fluoride water, and the silica was dissolved and removed over 6 hours, washed thoroughly with water and dried to obtain a porous polyimide film (RPIF-2).

<Comparative Example 3>
Example 3 except that a crosslinked polymethyl methacrylate copolymer (SSX-101: manufactured by Sekisui Plastics Co., Ltd.) having an average particle diameter of 1 μm was used as the non-crosslinked resin fine particles, and the solvent for removing the non-crosslinked resin particles was toluene. In the same manner as above, a porous polyimide film (RPIF-3) was obtained. When the crosslinked resin particles were used, the crosslinked resin particles did not dissolve in the solvent and swelled, but it was a film with many cracks.

[Evaluation of pore size distribution]
For the porous polyimide films obtained in Examples 1 to 5 and Comparative Examples 1 to 3, the pore size distribution was evaluated (maximum diameter, minimum diameter, average diameter, and ratio of major axis to minor axis). It was. Specifically, the evaluation was performed by the method described above.

[Evaluation of cracks]
The porous polyimide films obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were evaluated for cracks. The specific method is as follows. The above 0.1mm area of the polyimide film 1 cm ² square by microscope magnification 500 and cracking were visually observed whether.

-Evaluation criteria-
A: No crack B: 1 or more and 3 or less C: 4 or more

[Content of non-crosslinked resin other than polyimide resin]
By the method described above, the content of non-crosslinked resin other than the polyimide resin contained in the porous polyimide film was measured.

The details of the abbreviations in Table 1 are shown below.
“PDA”: p-phenylenediamine “BPDA”: 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride “MMO”: methylmorpholine “DMIz”: 1,2-dimethylimidazole “THF”: Tetrahydrofuran • “Tol”: Toluene • “PMMA / St”: Non-crosslinked polymethyl methacrylate / styrene copolymer • “Crosslinked PMMA”: Crosslinked polymethyl methacrylate copolymer • “IPA”: Isopropanol “NMP”: N-methylpyrrolidone

1 Non-crosslinked resin particles, 2 binder resin, 3 substrate, 4 release layer, 5 polyimide precursor solution, 7 pores, 61 polyimide film, 62 porous polyimide film

Claims (4)

  A porous polyimide film containing a polyimide resin and a non-crosslinked resin other than a polyimide resin and having a spherical pore.   2. The porous polyimide film according to claim 1, wherein the content of the non-crosslinked resin other than the polyimide resin is 0.1% by mass or more and 5% by mass or less with respect to the entire porous polyimide film.   The porous polyimide film according to claim 1 or 2, wherein the non-crosslinked resin other than the polyimide resin is a non-crosslinked resin soluble in a solvent that does not dissolve the polyimide resin. After forming a coating film containing a polyimide precursor solution in which a polyimide precursor is dissolved in an aqueous solvent and non-crosslinked resin particles not dissolved in the polyimide precursor solution, the coating film is dried, and the polyimide A first step of forming a coating comprising a precursor and the non-crosslinked resin particles;
The second step of heating the coating to imidize the polyimide precursor to form a polyimide film, and removing the non-crosslinked resin particles with an organic solvent that dissolves the non-crosslinked resin particles. A second step including:
The porous polyimide film as described in any one of Claims 1-3 obtained by the manufacturing method of the porous polyimide film which has this.